Medication adherence among gout patients initiated allopurinol: a retrospective cohort study in the Clinical Practice Research Datalink (CPRD)

Objectives: When urate lowering therapy is indicated in patients with gout, medication adherence is essential. This study assesses non-persistence and non-adherence in patients with newly diagnosed gout, and identifies factors associated with poor medication adherence.

Methods: A retrospective data analysis was performed within the UK Clinical Practice Research Datalink (1987-2014) among incident gout patients, aged ⩾40 years and starting allopurinol (n = 48 280). The proportion of patients non-persistent (a first medication gap of ⩾90 days) after 1 and 5 years, and median time until a first 90-day gap was estimated using Kaplan-Meier statistics in those starting allopurinol and restarting after a first interruption. Non-adherence (proportion of days covered <80%) over the full observation period was calculated. Multivariable Cox- or logistic regressions assessed factors associated with non-persistence or non-adherence, respectively.

Results: Non-persistence increased from 38.5% (95% CI: 38.1, 38.9) to 56.9% (95% CI: 56.4, 57.4) after 1 and 5 years of initiation. Median time until a first 90-day gap was 1029 days (95% CI: 988, 1078) and 61% were non-adherent. After a first gap, 43.3% (95% CI: 42.7, 43.9) restarted therapy within 1 year, yet only 52.3% (95% CI: 51.4, 53.1) persisted for 1 year. Being female and a current smoker increased the risk for non-persistence and non-adherence, while older age, overweight, receiving anti-hypertensive medication or colchicine and suffering from dementia, diabetes or dyslipidaemia decreased the risk.

Conclusion: Medication adherence among gout patients starting allopurinol is poor, particularly among females and younger patients and patients with fewer comorbidities. Medication adherence remains low in those reinitiating after a first gap.